Cardiac arrhythmias are a leading cause of stroke, heart disease and sudden death. The physiological mechanism of arrhythmia involves an abnormality in the electrical conduction of the heart. There are a number of treatment options for patients with arrhythmia which include medication, implantable devices, and minimally invasive procedures.
Minimally invasive procedures, such as catheter ablation, have evolved in recent years to become an established treatment for patients with a variety of supraventricular and ventricular arrhythmias. A typical minimally invasive procedure involves mapping of the heart tissue in order to identify the site of origin of the arrhythmia followed by a targeted ablation of the site. Other minimally invasive procedures involve the delivery of biological agents such as cells or genes as a form of therapy to the identified site of origin of the arrhythmia. The procedure takes place in an electrophysiology laboratory and takes several hours, most of which is spent mapping the electrical conduction in the heart.
Conventional 3D mapping techniques include contact mapping and non-contact mapping. In contact mapping techniques one or more catheters are advanced into the heart. Physiological signals resulting from the electrical activity of the heart are acquired with one or more electrodes located at the catheter distal tip after determining that the tip is in stable and steady contact with the endocardium surface of a particular heart chamber. Location and electrical activity is usually measured sequentially on a point-by-point basis at about 50 to 200 points on the internal surface of the heart to construct an electro-anatomical depiction of the heart. The generated map may then serve as the basis for deciding on a therapeutic course of action, for example, tissue ablation, to alter the propagation of the heart's electrical activity and to restore normal heart rhythm.
Although the electrode(s) contacting the endocardium surface enable a relatively faithful acquisition of physiological signals with minimal signal degradation, contact-based mapping techniques tend to be time consuming since the catheter, and thus its electrodes, have to be moved to a relatively large number of locations in the heart cavity to acquire sufficient data to construct the electro-anatomical depiction of the heart. Additionally, moving the catheter to different locations so that the catheter's electrode(s) touch the endocardium is a cumbersome process that is technically challenging. Further complicating the contact-based mapping methodology is the occurrence of unstable arrhythmias condition. Particularly, ventricular tachyarrhythmias may compromise the heart's ability to circulate blood effectively. As a result, the patient cannot be maintained in fast tachyarrhythmia's for more than a few minutes, which significantly complicates the ability to map during the arrhythmia. In addition, some arrhythmia's are transient or non-periodic in nature. Contact-based sequential mapping, therefore, is less suitable for mapping these arrhythmia's since the sequential contact-based methodology is predicated on the assumption that recorded signals are periodic in nature.
On the other hand, in non-contact-based mapping systems a multiple electrodes catheter is percutaneously placed in the heart chamber of interest. Once in the chamber, the catheter is deployed to assume a 3D shape. Using the signals detected by the non-contact electrodes and information on chamber anatomy and relative electrode location, the system provides physiological information regarding the endocardium of the heart chamber. Although non-contact mapping techniques can simultaneously acquire signals using the multiple electrodes catheter and thus enable faster reconstruction of the electrical activity on the endocardial surface, because the catheter's multiple electrodes are not in contact with the endocardium surface some loss of accuracy of the reconstructed map, which is proportional to the distance from the endocardium, occurs due to the degradation of the signals acquired by the multiple electrodes. Moreover, the computation of the complex transformations required to transform the signals acquired by the catheter's electrodes to determine the corresponding reconstructed information at the endocardium surface is relatively time consuming. Also, the accuracy of the reconstructed information is constrained by the number of electrodes that can be attached to the catheter.